376 PHILOSOPHY OF ZOOLOGY. 
MER, and others, on the human body, it appears to vary 
greatly, being, in the same individual, sometimes pesitive 
and at other times negative, and lable to sudden change, 
upon any quick motion being performed. In making these 
observations, there is some difficulty in avoiding the effects 
of friction of the cloth, and other circumstances foreign 
to the natural state of the body. 
III.—AnmmAt Heat. 
In every animal there is a certain degree of heat neces- 
sary to its existence, and the full exercise of its functions. 
In quadrupeds and _ birds this heat is considerably great- 
er, in general, than the surrounding atmosphere, while in 
fishes and the animals of the inferior classes, it 1s seldom 
very different from the temperature of the objects with 
which they are usually in contact. The ordinary temperature 
of the human body is rated at between 96° and 98° of F. 
In the common hen, the temperature is between 103° and 
104°. Those animals whose temperature is high, and not 
greatly influenced by the changes in the heat of external 
objects, are denominated warm-blooded animals. 'Those, 
on the other hand, whose temperature is greatly influenced 
by that of surrounding objects, are termed. cold-blooded 
animals. In both classes, the temperature is regulated by 
the vital powers of the animals, and limits are assigned be- 
yond which it is dangerous to pass. The range of warm 
blooded animals is confined, that of the cold blooded exten- 
sive. Both, however, are influenced by the same agents, 
and appear to be governed by the same general laws. 
1. When an animal is exposed to a change of tempera- 
ture, some corresponding change likewise takes place in 
the heat of its body.—The propriety of establishing this 
general law, is sanctioned by the experience of our own 
